The capturing of astronomical images by using long exposure image capture techniques has long been known in the arts. When used in a telescope configuration, an imaging device such as a film camera or digital camera is mounted to a telescope having a defined field of view. The field of view used to capture an astronomical image is generally defined by the size and optics of a given telescope including the viewing aperture in the telescope body.
Due primarily to the rotation of the earth relative to the star or celestial body desired to be imaged, there has been development of various guide star tracking techniques. In a simple telescope configuration, a second guide scope is mounted in parallel with the main scope in order to locate a guide star within a portion or near the field of view of the main scope used for imaging. In more sophisticated configurations, a guide sensor is rigidly mounted off-axis within the housing body of the main scope. In such configurations, an imaging sensor (e.g. a charged-coupled device (CCD) sensor) is mounted near the center of the housing at a distal end opposite the opening aperture of the housing. In addition, there is a reflective member rigidly mounted (e.g. at a 45 degree angle) but adjacent to the imaging sensor. The reflective member directs light toward a second sensor (e.g. a CCD sensor) used for tracking a guiding object (e.g. a guide star). This configuration allows the guiding image to view a tracking star just outside of the field of view of the imaging sensor. Such a configuration allows for tracking a guide star in the periphery of the imaging sensor field of view (i.e. off-axis guiding) and is disclosed in issued U.S. Pat. No. 5,525,793.
One disadvantage of prior art devices is that the accessible field of view is quite limited. Such a drawback makes it difficult to locate a guide start bright enough, thus making finding a usable guide star challenging and time consuming. When using a second scope for guiding, there is an ability to have a larger field of view, however mirror motions and mechanical flexure differences between the guide scope and the main scope result in limits for medium and short imaging exposures.